Early Development

Week 1


Ovulation releases ovum/secondary oocyte


Fertilisation in the oviduct produces zygote

As zygote moves along oviduct > produces morula

- As zygote divides, cells become smaller

- Movement by cilia and peristalsis present in oviduct walls


Morula develops into a blastocyst

- Trophoblast (outer layer of blastocyst) nourishes future embryo

- Inner cell mass will become foetus

- Fluid filled cavity for protection (absorbs shocks, resists compression, ...)


Blastocyst (?100cells) implants itself in uterus lining

- Nourished by secretion from uterus

- Microvilli provide large surface area (? gas + nutrients exchange)

Week 2

Trophoblast secretes enzymes ? digest tissues and blood vessel of endometrium

Embryo uses released nutrients/products from digestion

Blastocyst becomes buried within endometrium

Microvilli are replaced by placenta

Trophoblast secretes human chorionic gonadotrophin (hCG) hormone

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